The art of laser welding is relatively well known. In general, with reference to FIG. 1A, first and second work pieces, embodied as an upper work piece 100 laid on a lower work piece 120 along a weld interface 180, become welded to one another by way of an irradiated beam 140 of laser light. As is known, the beam 140 passes through the upper work piece, which is transparent to laser light, where it gets absorbed by the lower work piece, which is laser light absorbent. As the beam irradiates, the weld interface heats up and causes the bottom surface of the upper work piece and the upper surface of the lower work piece to melt. Upon cooling, the two work pieces meld together. An optical path between a laser light source (not shown) and the to-be-welded work pieces may include a lens 160, for proper focusing, or other optical elements, such as mirrors, fiber optic strands, scanning structures. A clamping device (not shown) typically provides a pressing engagement of the work pieces to maintain relative positioning and good surface contact during welding.
In instances when the upper work piece prevents sufficient amounts of laser light from arriving at the weld interface, poor welding (underweld) results. In instances when the upper work piece absorbs too much energy, the upper work piece often overheats and/or suffers material degradation which potentially causes aesthetic problems as well as unsatisfactory welds. Numerous parameters contribute to the absorption and transmission characteristics of materials including, but not limited to, laser wavelength, incident angle of the laser beam, surface roughness of the work piece, temperature of the work pieces, thickness/dimensions of the work piece, composition of the work piece and, in the instance when the work pieces comprise plastics, additives such as flame retardants, plasticizers, fillers and colorants.
Yet, when the material properties and laser properties become fixed in a given system, the transmission rate of the laser through a work piece follows the well known Beer-Lambert Law, specifically: I/Io=e(−sx); where Io is the intensity of the light source incident on the work piece, I is the intensity of the light after passing through the work piece, x is the thickness of the work piece, and s is the total extinction coefficient which, in turn, is the work piece light scattering coefficient plus the work piece light absorption coefficient. Accordingly, the thickness of the work piece (variable x) constitutes an important variable in light transmission rates.
As is apparent in FIG. 1A, the upper work piece 100 comprises a generally uniformly thick material. Thus, laser light will transit the work piece in area A at substantially equivalent rates as compared to area B, or any other area of the work piece, which will likely result in generally uniform weld joint along the weld interface.
With reference to FIG. 1B, however, sometimes the upper work piece 200 does not embody a uniformly thick structure and laser light transmission rates will not compare favorably between regions 220, 222 and 224, for example, resulting in a weld joint at the weld interface 180 that likely lacks uniformity in thickness and/or strength. It may even lead to compromised structural integrity.
Present solutions to overcome this problem, in the instance of a sweeping laser in contour welding, include moving the laser slower in relatively thicker regions 220 or faster in relatively thinner regions 224 or, in the instance of simultaneous welding, increasing the laser power in thick regions 220 or decreasing laser power in thin regions 224. Both of these approaches, however, lack practicality. For example, a sweeping laser suffers from inertia effects during periods of acceleration and deceleration and a variable laser power requires additional laser controllers which add complexity and cost.
Accordingly, a need exists in the laser welding arts for economically and efficaciously laser welding two work pieces even when one of the to-be-welded work pieces embodies a non-uniformly thick dimension.
Regarding the technology of inkjet printing, it too is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium, such as a sheet of paper, at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at such times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, masking and etching techniques on a substrate such as silicon.
To print or emit a single drop of ink, an individual heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.
During manufacturing of the printheads, a printhead body gets stuffed with a back pressure device, such as a foam insert, and saturated with mono or color ink. A lid welds to the body via ultrasonic vibration. This, however, has sometimes caused cracks in the heater chip, introduced and entrained air bubbles in the ink and compromised overall printhead integrity.
Even further, as demands for higher resolution and increased printing speed continue, heater chips are often engineered with more complex and denser heater configurations which raises printhead costs. Thus, as printheads evolve a need exists to control overall costs, despite increasing heater chip costs, and to reliably and consistently manufacture a printhead without causing cracking of the ever valuable heater chip.